The present invention relates to a liquid crystal display device, and, more particularly, to a technology applicable to image signal line driving (drain driver) of a liquid crystal display device which is capable of producing a multiple grayscale display.
An active matrix type liquid crystal display device having an active element (for example, thin film transistor) for each pixel, and in which a display is produced by selectively driving the active elements, is widely used as a notebook type personal computer. In the active matrix type liquid crystal display device, an image signal voltage (grayscale voltage in correspondence with display data; hereinafter, referred to as a grayscale voltage) is applied via the active element; and, accordingly, there is no cross talk among respective pixels, so that it is not necessary to use a special drive method for preventing cross talk as in a simple matrix type liquid crystal display device, whereby multiple grayscale display is feasible.
As one known example of the active matrix type liquid crystal display device, there is a liquid crystal display device having a liquid crystal display panel (TFT-LCD) of the TFT (Thin Film Transistor) type, a drain driver arranged on an upper side of the liquid crystal display panel, a gate driver arranged at a side face of the liquid crystal display panel and an interface unit. According to the TFT type liquid crystal display device, there are provided a grayscale voltage generating circuit, a grayscale voltage selecting circuit (decoder circuit) for selecting one grayscale voltage in correspondence with display data from among a plurality of grayscale voltages generated in the grayscale voltage generating circuit and an amplifier connected to receive the one grayscale voltage selected by the grayscale voltage selecting circuit. Such a technology is described in, for example, Japanese Application No. 8-86668.
In recent years, in a liquid crystal display device of a liquid crystal module of the TFT type, along with demands for a large screen liquid crystal display panel, there is a further demand for a high resolution formation, such as 1024xc3x97768 pixels in the XGA display mode, 1280xc3x971024 pixels in the SXGA display mode or 1600xc3x971200 pixels in the UXGA display mode. Therefore, the number of horizontal scans in one vertical scan period is increased; and, in accordance therewith, the write time period per one horizontal scan become shorter and shorter, and so the output delay time period (tDD) of the drain driver poses a serious problem.
For example, in the XGA display mode, the write time period per one horizontal scan is about 20 xcexcs, and there is also a case in which the output delay time period (tDD) of the drain driver reaches 10 through 20 xcexcs. In such a case, the pixel write voltage becomes deficient and the display quality of the image displayed on the liquid crystal display panel is significantly deteriorated.
Meanwhile, in a liquid crystal display device, there is a tendency toward large size formation and high resolution formation (multiple pixel formation). Furthermore, in order to dispense with wasteful space and produce a display device having an attractive appearance, a region other than a display region of the liquid crystal display device, that is, a frame edge portion thereof, should be reduced in size (narrow frame edge formation). For that purpose, it is necessary to further reduce the chip size of a semiconductor chip constituting a drain driver; and, in accordance therewith, the grayscale voltage selecting circuit has been constituted by a field effect type transistor (MOS transistor) of a minimum size. As a result, the current driving function of the grayscale voltage selecting circuit is lowered, and the time period (output delay time period) for determining the grayscale voltage in correspondence with display data by the grayscale voltage selecting circuit is increased, which constitutes a significant factor in the output delay time period (tDD) of the drain driver.
Further, in a liquid crystal display device, the multiple grayscale display is being advanced from a 64 value grayscale display to a 256 value grayscale display, and the voltage width per grayscale value of a plurality of grayscale voltages generated by the grayscale voltage generating circuit (that is, potential difference between contiguous grayscale voltages) is reduced. Meanwhile, with respect to an amplifier for amplifying the grayscale voltage, owing to a dispersion in the characteristic of the active element constituting the amplifier, an offset voltage is produced; and, when the offset voltage is produced in the amplifier, an error is caused in the output voltage of the amplifier, and the output voltage of the amplifier becomes a voltage different from a target value (regular grayscale voltage). This results in a problem in which a vertical streak of black or white is produced on the display screen displayed on the liquid crystal display panel, which significantly deteriorates the display quality.
The invention has been carried out in order to resolve the above-described problems of the conventional technology, and it is an object of the invention to provide a technology capable of promoting the display quality of a display image displayed on a liquid crystal display element in a liquid crystal display device.
It is another object of the invention to provide a technology enabling high speed operation and large screen formation of a liquid crystal display element in a liquid crystal display device.
The objects and novel characteristics of the invention will become more apparent from the following description and the attached drawings.
A simple explanation will be given of representatives features of the invention disclosed in the specification.
That is, according to an aspect of the invention, there is provided a liquid crystal display device comprising a liquid crystal display element having a plurality of pixels provided in a matrix arrangement and a plurality of image signal lines for applying grayscale voltages in correspondence with display data to respective pixels in a column (or row) direction to the plurality of pixels, and image signal line driving means constituted by at least a single semiconductor integrated circuit device for supplying the grayscale voltages in correspondence with the display data to the respective image signal lines. The semiconductor integrated circuit device comprises a plurality of grayscale voltage selecting means for selecting the grayscale voltages in correspondence with the display data inputted from the plurality of grayscale voltages and constituted by a transistor having a minimum size in the semiconductor integrated circuit device; a plurality of amplifiers for amplifying the grayscale voltages selected by the respective grayscale voltage selecting means and for outputting the selected grayscale voltages to the respective image signal lines; first switching means provided between the respective grayscale voltage selecting means and the amplifiers; second switching means provided between a power source line supplied with a predetermined charge voltage and the respective amplifiers; and switching controlling means for switching off the first switching means and switching on the second switching means in an initial predetermined time period of one horizontal scanning time period.
Further, according to another aspect of the invention, there is provided a liquid crystal display device comprising a liquid crystal display element having a plurality of pixels provided in a matrix arrangement and a plurality of image signal lines for applying grayscale voltages in correspondence with display data to respective pixels in a column (or row) direction to the plurality of pixels, and image signal line driving means constituted by at least a single piece of a semiconductor integrated circuit device for supplying the grayscale voltages in correspondence with the display data to the respective image signal lines. The semiconductor integrated circuit device comprises a plurality of grayscale voltage selecting means for selecting the grayscale voltages in correspondence with the display data inputted from the plurality of grayscale voltages and constituted by a transistor having a minimum size in the semiconductor integrated circuit device; a plurality of amplifiers for amplifying the grayscale voltages selected by the respective grayscale voltage selecting means and outputting the selected grayscale voltages to the respective image signal lines, the plurality of amplifiers including switching means for switching one of a pair of two terminals of each of the amplifiers to an inverted input terminal or a noninverted input terminal and switching other of the pair of two terminals to the noninverted input terminal or the inverted input terminal; first switching means provided between the respective grayscale voltage selecting means and the respective amplifiers; second switching means provided between a power source line supplied with predetermined charge voltage and the respective amplifiers; switching controlling means for switching off the first switching means and switching on the second switching means in an initial predetermined time period in one horizontal scanning time period; and switching instructing means for outputting a switch control signal for switching one of the pair of input terminals of each of the amplifiers to the noninverted input terminal and switching other input terminal thereof to the inverted input terminal to the switching means of the amplifiers at every predetermined period.
Further, according to another aspect of the invention, there is provided a liquid crystal display apparatus, wherein the switching controlling means switches off the first switching means before for switching on the second switching means and switching on the first switching means after switching off the second switching means.
Further, according to another aspect of the invention, there is provided a liquid crystal display device, wherein the switching controlling means controls the first and the second switching means based on a clock for controlling an output timing and a clock for latching the display data.
Further, according to another aspect of the invention, there is provided a liquid crystal display device, wherein the predetermined charge voltage is any voltage in the plurality of grayscale voltages.
Further, according to another aspect of the invention, there is provided a liquid crystal display device, wherein the semiconductor integrated circuit device includes grayscale voltage generating means for generating the plurality of grayscale voltages based on a plurality of grayscale reference voltages supplied from outside and supplying the plurality of grayscale voltages to the respective grayscale voltage selecting means, and wherein the predetermined precharge voltage is any voltage in the plurality of grayscale reference voltages supplied from outside.
Further, according to another aspect of the invention, there is provided a liquid crystal display device, wherein, when in the plurality of grayscale voltages supplied to one side of a liquid crystal layer of each of the plurality of pixels, the grayscale voltage having the largest potential difference relative to an opposed voltage applied to the other side of the liquid crystal layer of each of the plurality of pixels constitutes a maximum grayscale voltage and the grayscale voltage having the smallest potential difference relative to the opposed voltage constitutes the smallest grayscale voltage, the predetermined charge voltage is a voltage deviated to the maximum grayscale voltage in comparison with an intermediate voltage between the maximum grayscale voltage and the minimum grayscale voltage.
Further, according to another aspect of the invention, there is provided a liquid crystal display device, wherein the plurality of amplifiers comprise a plurality of couples of amplifier couples constituted by first amplifiers couples of which output grayscale voltages having a positive polarity and second amplifiers couples of which output grayscale voltages having a negative polarity, wherein the grayscale voltage selecting means connected to the first amplifiers of the respective amplifier couples select grayscale voltages in correspondence with display data inputted from the plurality of grayscale voltages having a positive polarity, wherein the grayscale voltage selecting means connected to the second amplifiers of the respective amplifier couples select grayscale voltages in correspondence with the display data inputted from the plurality of grayscale voltages having a negative polarity, further comprising display data switching means for switching alternately arbitrary couples of display data inputted to the grayscale voltage selecting means connected to the first amplifiers of the respective amplifier couples and the grayscale voltage selecting means connected to the second amplifiers of the respective amplifier couples, and image signal line switching means for switching alternately the couples of grayscale voltages outputted from the respective amplifier couples in accordance with switching of the display data switching means and outputting the couples of grayscale voltages to arbitrary couples of the image signal lines.